Field of the Invention
This invention relates to a method of fracturing a geothermal formation. More particularly, this invention relates to a fracturing method in which the fracturing fluid includes a metal-plated propping agent coated with a thermoplastic polymer.
Prior Art
One of the major sources of energy in the world is the natural heat of the earth. A number of attempts have been made to recover heat from the geothermal formations or hot formations of the earth; however, only an extremely small quantity of energy compared to the total amount consumed is derived from this source at the present time. In California alone over 1 million acres of land are classified as being in geothermal resource areas. Steam derived from geothermal sources is being employed in the United States, Italy, Mexico, Russia, New Zealand and Japan to drive turbines for electrical power generation. In Iceland, hot water derived from hot artesian wells or springs is transmitted through pipes and utilized in heating buildings and greenhouses.
The desirability of utilizing heat derived from a geothermal source is apparent since the fossil fuel sources, i.e., coal, oil, peat, etc. are limited and can be exhausted within a few decades at the present rate of production.
All of the installatins in operation today employing energy derived from geothermal sources operate with hot water and/or steam derived from geothermal formations into which underground water flows and becomes heated. One of the most successful geothermal installations is that operated in Northern California to produce electricity. In this geothermal reservoir subterranean water contacting the hot reservoir rock structure is flashed into steam forming a very large steam reservoir at temperatures of the order to 500.degree.-550.degree. F. or more while shut-in pressure of the wells below 2000 feet is 450-480 psig.
The use of steam and/or hot water produced in geothermal reservoirs suffers from several major disadvantages. Frequently, large volumes of noxious gases such as hydrogen, sulfide, carbon dioxide, hydrocarbons, ammonia, etc. are produced with the steam or water and these gases must be removed and disposed of in a manner which will not pollute the environment. The mineral content of the steam and/or water recovered from any geothermal wells is so high that the steam recovered may be so corrosive as to preclude its use in turbines, etc. In most instances where water is recovered with the steam, the salinity is usually of such magnitude that the cool brine can be discharged to surrounding streams or lakes only after being treated to reduce the salinity to an acceptable value. Furthermore, many plants which utilize steam from geothermal reservoirs for turbine power generation discharge a condensate from the condensers which is so high in boron that the toxic effluent must be sent to an appropriate treatment plant or returned to the underground reservoir through a disposal well.
There is a definite need in the art therefore for a process in which energy in the form of heat can be recovered from a geothermal formation without the removal from the formation of substantial quantities of the highly corrosive brines associated with these formations. Among the advantages of such a process are: (1) subsidence of the producing area would be prevented and (2) the heat transfer medium, i.e., the brine, would be retained in the formation.
There is a definite need in the art for a low friction loss method of fracturing geothermal formations in which the propping agents included with the fluid employed in the fracturing process also will serve to improve the rate of heat transfer between the hot formation and the fluid therein